A systematic review and meta-analysis depicted that there is a substantial correlation between exposure to fine particulate matter (PM2·5) and the incidence of dementia. However, there is no substantial link of dementia with nitrogen oxides (NOX), nitrogen dioxide (NO2), and ozone (O3) exposure. Ehsan Abolhasani et al. aimed to evaluate the correlation between dementia and air pollution.

To incorporate population-based cohort studies that investigated the hazard ratio (HR) of dementia in people over 40 years of age in relation to exposure to O3, NO2, NOX, or PM2.5, databases such as Web of Science, Scopus, PsycINFO, EMBASE, MEDLINE, and PubMed were explored. Two researchers independently collected the data. The pooled HR for dementia per unit of pollutant was the primary endpoint ascertained, which was determined utilizing a random-effects model. The results were presented in compliance with PRISMA standards.

The systematic review included 20 studies in total, of which 17 provided information for the meta-analysis.  There were 91,391,296 people in total who were incorporated, and 5,521,111 (6%) of them had been diagnosed with dementia. The meta-analyses of PM2.5, NOX, NO2, and O3 comprised a total of 12, 5, 6, and 4 trials, respectively. Every 1 μg/m3 rise in PM2.5 was associated with a 3% increase in the risk of dementia (HR, 1.03; I2 = 100%).

It was less obvious if dementia increased with each 10 μg/m3 increase in NOX (HR, 1.05; I2 = 61%), NO2 (HR, 1.03; I2 = 94%), or O3 (HR, 1.01; I2 = 82%) levels, while a substantial connection could not be ruled out.  Across the studies, there was also considerable heterogeneity. To sum up, there was a non-significant connection between dementia and NOX, NO2, and O3 exposure and a substantial link between exposure to PM2.5 and dementia incidence.